p p m m o o d d t t m m p p 2 2 ? ? r r e e f f e e r r e e n n c c e e m m a a n n u u a a l l revision: october 11, 2011 1300 ne henley court, suite 3 pullman, wa 99163 (509) 334 6306 voice | (509) 334 6300 fax doc: 502-221 page 1 of 2 copyright digilent, inc. all rights reserved. other product and company names mentioned may be tradema rks of their respective owners. overview the PMODTMP2 is a temperature sensor and thermostat control board built around the analog devices adt7420. features include: ? up to 16-bit resolution ? typical accuracy better than 0.25 c ? i 2 c interface with 4 selectable addresses ? 240ms continuous conversion time ? support for 3.3v and 5v interfaces ? no calibration required ? programmable overtemperature/undertemperature control pins. functional description the PMODTMP2 uses an 8-pin connector that allows for communication via i 2 c, and provides pins to daisy-chain the PMODTMP2 to other i 2 c devices. the PMODTMP2 also provides two 2- pin headers for selecting the i 2 c address of the chip, and two 2-pin headers for controlling external devices based upon temperature thresholds defined by the user in software. i 2 c interface the PMODTMP2?s onboard adt7420 chip acts as a slave device using the industry standard i 2 c communication scheme. to communicate with the PMODTMP2 device the i 2 c master device must specify a slave address (0x48- 0x4b) and a flag indicating whether the communication is a read (1) or a write (0). this is followed by the actual data transfer. for the adt7420, the data transfer should consist of the address of the desired device register followed by the data to be written to the specified register. to read from a register the master must write the desired register address to adt7420, then send an i 2 c restart condition, and send a new read request to the adt7420. if the master does not generate a restart condition prior to attempting the read, then the value written to the address register will be reset to 0x00. as some registers stored 16-bit values as 8-bit register pairs, the adt7420 will automatically increment the address register of the device when accessing certain registers such as the temperature registers and the threshold registers. this allows for the master to use a single read or write request to access both the low and high bytes of these registers. a complete listing of registers and their behavior can be found in the adt7420 datasheet available on the analog devices web site. the i 2 c interface standard uses two signal lines. these are i 2 c data and i 2 c clock. these signals map to the serial data (sda) and serial clock (scl) respectively on the adt7420. connector j1 ? i2c communications pin signal description 1, 2 scl i2c clock 3, 4 sda i2c data 5, 6 gnd power supply ground 7, 8 vcc power supply (3.3v/5v) interface connector signal description
PMODTMP2 reference manual www.digilentinc.com page 2 of 2 copyright digilent, inc. all rights reserved. other product and company names mentioned may be tradema rks of their respective owners. i 2 c address selection the PMODTMP2 i 2 c bus can be set to use one of four valid addresses. the top five bits of the address are fixed, and the two least significant bits are taken from the jumper states of jp2 and jp1. jp2 corresponds to bit one of the address while jp1 corresponds to bit zero. an open jumper corresponds to a one in the address while a shorted jumper corresponds to a zero. for example, when jp2 and jp1 are open the device uses the address 0x4b (0b1001011). open drain outputs the PMODTMP2 provides two open drain output headers for controlling external devices based upon current temperature thresholds. if the temperature leaves a range defined by registers t low (0x06:0x07) and t high (0x04:0x05) then the int pin on j3 can be driven low or high based upon the configuration of the device. similarly, the ct pin on j2 can be driven low or high if the temperature exceeds a critical threshold defined in t crit (0x08:0x09). both of these pins are pulled up by 10kohm resistors when they are not driven by the device. for details on their electrical specifications and configuration of the int and ct pins please refer to the adt7420 datasheet. quickstart operation when the PMODTMP2 is powered up, the onboard adt7420 is in a mode that can be used as a simple temperature sensor without any initial configuration. by default, the device address register points to the temperature msb register, so a two byte read without specifying a register will read the value of the temperature register from the device. the first byte read back will be the most significant byte (msb) of the temperature data, and the second will be the least significant byte (lsb) of the data. these two bytes form a two?s complement 16-bit integer, if the result is shifted to the right three bits and multiplied by 0.0625 the resulting signed floating point value will be a temperature reading in degrees celsius. for information on reading and writing to the other registers of the device, as well as notes on the accuracy of the temperature measurements please refer to the adt7420 datasheet. addresses jp2 jp1 address open open 0x4b (0b1001011) open shorted 0x4a (0b1001010) shorted open 0x49 (0b1001001) shorted shorted 0x48 (0b1001000)
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